1. Field of the Invention
The present invention relates generally to medical equipment, and more particularly to an intravenous fluid heating system including heat delivery along a length of tubing prior to introduction of the fluid into the patient to maintain and control an elevated fluid temperature.
2. Description of Related Art
Normothermia for humans is 37xc2x0 C. (98.6xc2x0 F.). When the body temperature falls below 36xc2x0, clinicians refer to the condition as hypothermic. Except for those rare procedures where hypothermia is a planned and carefully controlled surgical tactic for protecting the patient (e.g., open heart surgery and some neurosurgery), hypothermia is regarded as generally a disfavored, uncontrolled, and unintentional byproduct of medical procedures. However, the occurrence of hypothermia in post surgical recovery rooms can be as high as 60% to 70%. The outward manifestations of hypothermia can be shivering and discomfort, and the condition car lead to further complications.
There are many known contributing factors to post-surgical hypothermia. Cold operating rooms contribute to the patient""s loss of heat. Most ORs are kept colder than normal rooms, typically maintaining a maximum temperature of 20xc2x0 C. Another factor is the patient""s lack of clothing during a surgical procedure. Many times a patient will be exposed to the cold operating room with at most a flimsy gown, and in some instances the patient is predominantly exposed during what can be a lengthy procedure. Evaporation of fluids applied to the body such as Iodine can further rob the patient""s body of heat. Another significant loss of heat can be the heat exchange between a body which has been opened, exposing the vital organs, and the surrounding environment. These factors contribute to the high incidence of a patient""s post-operative hypothermia.
An important contributor to the hypothermia problem is the introduction of intravenous (IV) fluids into the patient before, during, and after surgery. For example, blood products are stored in refrigerators at temperatures of 4xc2x0 C. prior to use, which is just above freezing. Other fluids such as saline or glucose solutions are stored at room temperature (20xc2x0 C.), which is approximately 17xc2x0 below the body temperature. When a cold fluid is introduced into the body, the body must work to bring the new fluid to the body""s operating temperature at the expense of other body functions. In doing so, the body cools below its initial temperature, with the amount of cooling dependent on the quantity and temperature of the fluid to be introduced. Large amounts of fluid or very cold fluids can cause the patient""s temperature to drop several degrees, thereby triggering hypothermia even without any other contributing factors. This effect is magnified in younger patients as well as the elderly. Thus, the introduction of blood and other IV solutions are a major contributor to the problem of hypothermia in post-surgical patients.
In recognition of this problem, the medical community has tried to implement blood warmers which preheat the blood prior to introduction of the blood into the patient. However, blood warmers have heretofore been an unsatisfactory solution to the problem. First, while the existing blood warmers add some heat to the blood prior to delivery, the blood is still delivered at a temperature colder than the 37xc2x0-38xc2x0 C. which is maintained by the human body. This is attributable to heat loss of the preheated blood in the line from the heater to the point of infusion, where the warm line gives off heat to the colder surrounding environment. If the flow rate of the fluid is slow, then more heat is lost during the exposure time between the heater and the infusion point.
The majority of prior art fluid warmers are limited by having the heated region separate from the point of infusion, where the heat source is separated by the venipuncture site by a length of IV tubing. The fluid cools down in the unheated line necessitating a higher initial temperature of the heated fluid. However, overheating the fluid can break down products in the fluid and in some cases render the fluid useless or unsafe. The cool-down is particularly severe at low flow rates where a long residency time in the post-heater connecting line results in heat energy loss that could be as much as the heat added. At higher flow rates, the heater response time of prior art heaters prevents rapid response to abrupt flow changes without overheating the fluid.
To offset the problem of heat loss in the tubing which transports the IV fluid from the heating unit to the patient, the present invention employs a tubing which comprises an internal heating web traversing the length of the tubing, which heats the fluid in the tubing and prevents the fluid from entering the patient below normothermia temperatures. In a preferred embodiment, the present invention includes proximal and distal sensors which evaluate the temperatures at the beginning of the tube and the point of delivery, thereby providing a feedback loop for controlling the temperature at the point of entry of the body. By placing a heating web inside the flow field of the moving fluid, the present invention advantageously heats the fluid more efficiently and more evenly than if the outer walls of the tubing were heated.